Process for selective partial hydrogenation of polyaromatic compounds



United States Patent W 3,344,200 PROCESS FUR SELECTIVE PARTIAL HY- DROGENATIDN 0F PGLYAROMATIC COMPOUNDS Milton M. Wald, Walnut Creek, and William E. Ross, El Cerrito, Califi, assignors to Shell Oil Company, New York, N .Y., a corporation of Delaware No Drawing. Filed Nov. 30, 1964, Ser. No. 414,890 12 Claims. (Cl. 260-667) This invention relates to hydrogenation of armoatics. In particular it relates to selective partial hydrogenation of aromatics with an aluminum halide-hydrogen iodide catalyst.

It has now been found that aromatic hydrocarbons having from 2 to 4 aromatic rings and 0 to 2 alkyl substituents can be selectively reduced to a compound having one aromatic ring with a catalyst comprising aluminum halide and H1. The reducing agent for the selective hydrogenation is HI, which is oxidized to elemental iodine. Iodine produced in the reaction can be reconverted to HI either externally or in situ; in a preferred aspect of the invention HI is regenerated in situ in the presence of hydrogen and a noble metal catalyst.

Aromatics suitable for selective partial reduction according to the invention are hydrocarbons having 2 to 4 aromatic nuclei and Oto 2 alkyl substituents of 1 to 4 carbons. Examples of these compounds are naphthalene, anthracene, phenanthrene, naphthacene, chrysene, triphenylene, pyrene, fluorene, methylnaphthalene, gammaethylanthracene, etc. Unsubstituted aromatics are preferred starting materials. In general, these compounds are reduced by the process of the invention to a mononuclear aromatic compound; for instance, naphthalene is reduced to tetrahydronaphthalene. When the aromatic compound is substituted, hydrogenation occurs principally in the substituted ring; this is surprising since with conventional hydrogenation catalysts, hydrogenation proceeds more readily in the unsubstituted ring. This indicates that the mechanism of hydrogenation with catalysts of the invention is different from that associated with conventional catalysts. For convenience, the invention will be described in terms of naphthalene reduction.

Suitable temperatures for effecting the partial reduction process of the invention are 50 C. to 200 C., preferably 75 C. to 150 C. Autogenous pressure is satisfactory unless H1 is regenerated in situ; in this case, hydrogen pressures of 100 to 3000 p.s.i., preferably 500 to 1500 p.s.i., are used. The reaction is carried out in the liquid phase, and may optionally be conducted in an inert solvent such as a saturated hydrocarbon or a halogenated aromatic (e.g. dichlorobenzene). Reaction times are not critical and usually range from 0.1 to 10 hours.

The reducing agent of the invention is a combination of aluminum halide and HI. Preferred aluminum halides are chloride, bromide, and iodide; aluminum chloride is preferred. The aluminum halide is used in an amount of from about 0.5% to about 20%, preferably 1-5% by weight of hydrocarbon processed. Hydrogen iodide is generally present in an amount of from 0.5 to 200%, preferably 5 to 100% by weight of the hydrocarbon to be reduced, subject to upper concentration limitations when a noble metal hydrogenation catalyst is also used, discussed below.

When naphthalene is reduced by HI, iodine is formed according to the following equation:

3,344,200 Patented Sept. 26, 1967 Since HI is consumed in the reaction, it is necessary to provide a method of regenerating the HI from I This can be accomplished either by separation of the I formed, e.g., by extraction, distillation, or crystallization, and subsequent external hydrogenation, or by in situ regeneration with a noble metal catalyst. The noble metal catalyst used to regenerate HI includes a catalytically effective amount of a noble or platinum group metal, preferably supported on an inert carrier such as alumina, magnesia, boria, silica, zirconia, titani-a, and the like. A preferred catalyst base is alumina, preferably activated alumina. The catalyst generally contains about 0.01 to 10%, preferably 0.1 to 8% by weight of one or more of the platinum metals of Group VIII, i.e., platinum, palladium, rhodium, ruthenium, osmium, or iridium. The .preferred noble metal is platinum. The noble metal may be present in the metallic form or as a sulfide, oxide, or other combined form. If the noble metal is present in metallic form, it is preferably in very finely divided form, e.g., crystals of less than angstrom units size.

The supported noble metal catalyst can be prepared by any well-known technique. The metal can be directly deposited on the support, or may be added to the base precursor, e.g., to the alumina hydrate which is subsequently calcined. The catalyst base precursor is preferably an amorphous hydrous alumina, alumina monohydrate, alumina trihydrate, or their mixtures. The hydrate containing the metal can be dried and calcined at a temperature of 750 F. to 1200 F. or more.

When the supported metal catalyst is employed to reconvert I to HI, the concentration of HI maintained in the system is critical. It is surprising that even very small amounts of H1 can be tolerated in the system, because HI is a known poison for noble metal catalyst. However, it has been found that as long as the concentration of H1 is maintained below about 60 gms. HI/gm. noble metal, a satisfactory catalyst life is maintained. It is preferred to maintain a ratio of H1 to noble metal between about 5 to about 50, preferably 10 to about 30, grams HI per gram of noble metal.

Several experiments were conducted to illustrate the selective reduction reaction of the invention. Naphthalene was chosen as the aromatic compound to be reduced. The general procedure used in each of the experiments was as follows: the solid and liquid components of the reaction mixture were loaded into a clean, ovendried, 300 ml. stirred Hastelloy autoclave in a nitrogen-filled dry box. The reactor was sealed and attached to the autoclave assembly which comprised a pressure-gas manifold, autoclave stand, air-driven stirrer and pressure transducer. Gaseous components of the reaction mixture were pressured in from feed vessels mounted on a metrogram balance. The stirrer was activated to 900 r.p.tn., and the autoclave was heated to the desired temperature. Reactor pressure was continuously recorded, via a pressure transducer, on a Brown recorder. After the heating period was complete, the reactor was cooled in an ice bath, and gaseous products were vented through a gas scrubber which contained a known amount of caustic. Amounts of iodine produced were measured by extracting the product with a known amount of aqueous stannous chloride solution. Organic products were analyzed by gas-liquid chromatography using a 25-foot silicon oil column.

Results of various experiments in which naphthalene was selectively hydrogenated to tetrahydronapthalene are shown in Table I below. Reaction conditions were 100 C. and 400-800 p.s.i.g. H 50 m1 of o-dichlorobenzene was used as solvent for each run.

Table I.Selective reduction of naphthalene Run No 1 2 3 4 5 6 i 7 Time, hr 2 2 2 10 2 2 2 Feed, mmoles:

R'fiphthalene f3 40 100 100 1( 100 100 Aldiilii n 1611:1111: "iii ""16 I 200 200 40 40 40 40 40 5% Pt/AlzOa, grams 1 5 5 5 5 5 Rate of gas uptake, IHBJL, lb./hr. 51 120 88 120 160 355 1, 670 Total H2 uptake, approx., mmoles 122 198 183 200 129 Products, relative yield:

Decalins Trace 0.1 0. 4 1. 3 0. 25 Tetralin 90 61.5 83.4 89 99.5 63 Naphthalene 10 38 16.3 10 0.25 32 Iodine iound,meq 137 134 0.5 4.7 0.5 6.2 Selectivity to tetrahydronaphthalene,

percenL- 100 -109 99.8 99.6 98.6 99.7 92.8 Oonversiompcrcent 90 100 (S2 8 90 99.7 68

H01. Several important conclusions are apparent from the re- Table 11.Continued at: time. 212513253 1113; int astate to the reducing agent. In each case the remarkable selectivity Onverslon Percent of the reduction is apparent; essentially no completely g ggg g;figggiggg gggi s tetmhydmmphthalene saturated product was formed and the product consisted i 1 h entirely of tetrahydronaphthalene, even though an excess From, t 15 tab 6 It appaient that at 1g of HI was used and the reaction time was considerably in convgrsgons i l i f selectgfilty excess of that required. This high selectivity persists even tetra y romp t a ene man-named About two't 0 the methyltetrahydronaphthalene formed were Z-methylat 100% naphthalene conversion.

The rocess of runs 1 and 2 has the disadvanta e of tetrahydronaphthalene, indicating that hydrogenation ocp g curs mainly in the substituted ring. This 15 in contrast to formmg large amounts of iodine (two moles for each mole results Obtained with other known hydrogenation cata naphthalene reduced) in the product requiring separalysts; for example, Fieser and Jones, J. Am. Chem. Soc., itti i tttt gitait i iitifitffiitlttfiiti my 3-7, which illustrate that the iodine produced in the aro- 3 i i 5 23 2 3 gg lggg if y roman t a matics reduction can be reconvcrted to HI in the presence 5 1 A process for selectively reducing an aromatic of hydrogen and a suliported noble P catalyst pound having from 2 to 4- nuclei and 0 to 2 alkyl substitu- Pt 9% i g i i i i cgngersion 29 selectwgigare cuts of 1 to 4 carbon atoms and mixtures thereof which g fi fgg g g i 3 22 355; a? $2: comprises contacting the aromatic compound with a catawa d t g CO v r i0 015 99 77 40 lytically elfcctiveamount of aluminum halide and HI fi fi ifi of I g g under hydrogenation conditions and recovering a partialthai when another hydrog eu halide (H EII) is substituted 1y ilydrlogenated Product having one ammanc nng per mo ecu e. 2:; 2 i g i i giii ggg g g ggigg 3215 5 322; 2. A process for selectively reducing an aromatic com- 3 and 4 witl'i Runs 5 find 6 shows the lar e increase in p i lgmng from; to i i nuclel and g to 2 a a y su stituents 0 mm to car on atoms an mixcompoun wit cata ytica y e ective amounts 0 au- 5523.an grams?a;.z azstama a g eg at o o an recovering par 1a y y roi i gfi g gg i gggs g: 2 genated products having one aromatic ring per molecule. (E "gi s P S u 1 e e 3. A process for selectively reducing an aromatlc comund ha from 2 t 4 n le and O to -2 alk l ub- TO illustrate the efiect of an alkyl group attached to an ituents i to 4 cargon a i m s and mixtures i hei'eo-f igl gg gi ggiggtgi g23 ;332:5 32g g gg which comprises contacting the aromatic compound with from about 0.5% to about 20% by weight of aluminum $62 3 ii g g p sgg g f i h gfig a 3 halide and a catalytically effective amount of HI in the liquid phase at 50-200 C. and at a hydrogen pressure chlorobenzene. Results of the experiment are tabulated of from about 100 to about 3000 psi, and recovering b partially hydrogenated products having one aromatic ring Table II.-Reduction o Z-meth lna hthalene Per moleculef y p 4. The process of claim 3 wherein the aromatic com- Fced, mmoles: pound to be hydrogenated is naphthalene and the hydro- A1Cl 1O genated product is tetrahydronaphthalene. HI 20D 5 5. The process of claim 4 wherein the aluminum halide C10H7CH3 40 is aluminum chloride. Products, relative amounts of C -C hydrocar- 6. A process for selectively reducing an aromatic combonsf' percent: pound having from 2 to 4 nuclei and 0 to -2 alkyl sub- Tetralin 20.8 stituents of 1 to 4 carbon atoms and mixtures thereof Naphthalene 2.1 which comprises contacting the aromatic compound with Z-Methyltetraihydronaphthalene 46.6 from 0.5% to about 20% by weight of aluminum halide 5- and 6-methyltetrahydronaphthalene 18.1 and about 5% to about 200% by weight of H1 in the A C tetrahydronaphthalene 5.3 liquid phase at a temperature of from about 50 C. to A C tetrahydronaphthalene 5.3 200 C. for from about 0.1 to 10 hours at a hydrogen C HqCH3 1.8 pressure of from about 3000 p.s.i., and recovering partially hydrogenated products having one aromatic ring per molecule.

7. A process for selectively reducing an aromatic compound having from 2 to 4 nuclei and 0 to 2 alkyl substituents of 1 to 4 carbon atoms and mixtures thereof Which comprises contacting the aromatic compound with catalytically efifective amounts of aluminum halide and HI under hydrogenation conditions in the presence of a noble metal hydrogenation catalyst in an amount such that concentration of HI does not exceed 60 grams HI per gram noble metal, and recovering partially hydrogenated products having one aromatic ring per molecule.

'8. The process of claim 7 wherein the aromatic compound is naphthalene and the hydrogenated product is tetrahydronaphthalene.

9. A process for selectively reducing an aromatic compound having from 2 to 4 nuclei and 0 to 2 alkyl substituents of 1 to 4 carbon atoms and mixtures thereof which comprises contacting the aromatic compound with 0.5 to about 20% by weight of aluminum halide and from about 0.5200% by Weight of hydrogen iodide in the liquid phase at a temperature of from about 75 C.150 C. at a hydrogen pressure of about 100-3000 p.s.i. in the presence of a supported noble metal hydrogenation catalyst having from about .01-10% by Weight of noble metal 25 on an inert support, said noble metal hydrogenation catalyst being present in an amount such that the Weight ratio of HI to noble metal does not exceed 60, and recovering a partially hydrogenated product having one aromatic ring per molecule.

10. The process of claim 9 wherein the aromatic compound is naphthalene and the hydrogenated product is tetrahydronaphthalene.

11. The process of claim 9 wherein the supported metal hydrogenation catalyst is platinum supported on activated aluminum.

12. The process of claim 11 wherein the aromatic compound is naphthalene and the hydrogenated product is tetrahydronaphthalene.

References Cited UNITED STATES PATENTS DELBERT E. GANTZ, Primary Exanriner. SAMUEL P. JONES, Examiner. 

1. A PROCESS FOR SELECTIVELY REDUCING AN AROMATIC CONPOUND HAVING FROM 2 TO 4 NUCLEI AND 0 TO 2 ALKYL SUBSTITUENTS OF 1 TO 4 CARBON ATOMS AND MIXTURES THEREOF WHICH COMPRISES CONTACTING THE AROMATIC COMPOUND WITH A CATALYTICALLY EFFECTIVE AMOUNT OF ALUMINUM HALIDE AND HI UNDER HYDROGENATION CONDITIONS AND RECOVERING A PARTIALLY HYDROGENATED PRODUCT HAVING ONE AROMATIC RING PER MOLECULE. 